Field of the Invention
The present invention relates to a fixed platen of an injection molding machine.
Description of the Related Art
FIG. 5 is a schematic view for illustrating the configuration of a conventional injection molding machine. In the injection molding machine, a mold clamping mechanism section 1 and an injection mechanism section 2 are opposed to each other on a base frame 4. In a nozzle touch mechanism 3 between the mold clamping mechanism section 1 and the injection mechanism section 2, a nozzle at the tip of a screw 17 is in close contact with a resin injection port of a fixed mold 7.
The mold clamping mechanism section 1 comprises a fixed platen 5 and a movable platen 6 arranged along a mold clamping axis. Tie rods 25 are passed through tie-rod insertion parts 24 of the fixed platen 5. Also for the movable platen 6, the fixed and movable platens 5 and 6 are mounted so that the movable platen 6 is movable along the mold clamping axis by passing the tie rods 25 through tie-rod insertion parts (not shown). A mold clamping space is defined between the fixed and movable platens 5 and 6. The fixed mold 7 is mounted on the mold-clamping-space side of the fixed platen 5. A movable mold 8 is mounted on the mold-clamping-space side of the movable platen 6.
The movable platen 6 is connected with a crosshead link 11, a toggle mechanism, which is connected to a nut for a ball screw 12. The axis of the ball screw 12 is driven by a servomotor 14 through a pulley or pulleys and a belt system 13. The fixed and movable molds 7 and 8 are opened and closed and mold clamping is performed by driving the servomotor 14 to advance and retreat the movable platen 6 relative to the fixed platen 5.
In the injection mechanism section 2, a resin material 9 stored in a hopper 26 is melted as it is fed forward relative to a cylinder by the rotation of the screw 17 caused by the rotation of a metering servomotor 15 and heating by a heater 10 and is pooled in place. The molten resin material 9 is injected into a cavity in the fixed mold 7 by rotating an injection servomotor 16 to advance the screw 17.
Thereafter, the resin material 9 is cured in the mold set by the mold clamping between the fixed and movable molds 7 and 8 and a molded article is molded. After the molding, the product is ejected by an ejector pin (not shown) or the like.
FIG. 6 is a perspective view showing the base frame 4 and the fixed platen 5 of the injection molding machine. The base frame 4 comprises two upper main pipes 32, which are arranged parallel to each other on the upper side, and two parallel lower main pipes 33 on the lower side. A space between the two upper main pipes 32 serves as a molded product chute opening 31.
The upper and lower main pipes 32 and 33 are connected by a plurality of vertical posts 34. The mold clamping mechanism section 1, injection mechanism section 2, and the like are supported by the upper and lower main pipes 32 and 33.
The fixed platen 5 is secured to the base frame 4. The fixed platen 5 is urged to tilt by a nozzle touch force generated when a nozzle on the distal end of the injection cylinder is brought into close contact during the molding and a mold clamping force generated by the mold clamping. In order to prevent the fixed platen 5 from tilting, the fixed platen 5 is secured to the steel material of the upper main pipes 32 of the base frame 4 by bolts or the like.
FIG. 8 shows an example of fixation of the fixed platen 5 of the conventional injection molding machine. The fixed platen 5 shown in FIG. 8 is firmly secured to the upper main pipes 32 of the base frame 4. Further, techniques disclosed in the following prior art patent documents are alternative fixing methods.
As shown in FIG. 9, Japanese Patent Application Laid-Open No. 2000-238100 discloses a technique in which a leg protruding from the main body of a fixed platen 5 is provided at a substantially central portion of the lower side of the fixed platen secured to a base frame.
Japanese Patent Application Laid-Open No. 2000-289069 discloses a technique in which a fixed platen is prevented from tilting by being supported by connecting a rib thereon and a prop on a base frame.
Japanese Patent Application Laid-Open No. 2003-25378 discloses a technique in which a fixed platen is prevented from falling down by extending a mounting surface of the fixed platen toward an injection device so that its extended portion can be secured to a frame by bolts.
Japanese Patent Application Laid-Open No. 2007-253532 discloses a technique in which legs having means for securing a fixed platen to a base frame are provided on bottom parts on opposite sides of the fixed platen and a fall prevention leg is provided on the central bottom part of the fixed platen.
In the technique shown in FIG. 8, the fixed platen 5 is firmly secured to the upper main pipes 32 of the base frame 4. If the fixed platen 5 thus secured is subjected to a mold clamping force, deformation of the lower part of the fixed platen 5 secured to the base frame 4 is suppressed due to the rigidity of the base frame 4, as shown in FIG. 7. Since the upper part is not secured, in contrast, the degree of deformation is asymmetric, so that the upper part may considerably bend in some cases. Therefore, elongation of the tie rods 25 also varies, so that the application of the mold clamping force to the fixed and movable molds 7 and 8 may possibly be uneven.
In the technique disclosed in Japanese Patent Application Laid-Open No. 2000-238100, vertical variation in deformation of the fixed platen 5 due to thermal expansion and mold clamping force is suppressed. Since the base frame 4 is expected to secure a wide product chute opening under a mold mounting portion, however, that part of the base frame 4 which lies below the mold clamping mechanism section 1 is lower in rigidity than end portions. Possibly, therefore, the resulting structure may be susceptible to falling caused by nozzle touching.